As a recording method utilizing the phase change, a method has been known wherein the crystal structure of a metal or a semiconductor is reversibly changed by affecting energy beams or an energy flow such as light or electric current (Joule heat) (Appl. Phys. Lett., Vol. 18 (1971), pp. 254–257, U.S. Pat. No. 3,530,441).
Used practically at present as a means for recording on an information recording medium employing a phase-change recording material, is a means to utilize a reversible change between the crystalline phase and the amorphous phase. Specifically, it is a means to let the crystalline state in a non-recorded/erased state and to form amorphous marks at the time of recording. Usually, a recording layer is locally heated to a temperature higher than the melting point and then rapidly cooled to form amorphous marks. On the other hand, the recording layer is heated at a temperature of approximately at most the melting point and at least the crystallization temperature, and slowly cooled so that the recording layer is kept at a temperature of at least the crystallization temperature for a certain retention time to carry out recrystallization. Namely, in general, a reversible change between the stable crystalline phase and the amorphous phase is utilized, and the information is recorded or retrieved by detecting the difference in physical parameters such as refractive index, electric resistance, volume and change in density, between the crystalline state and the amorphous state.
On the optical information recording medium among information recording mediums, recording/retrieving is carried out by utilizing a change in the reflectivity accompanying the reversible change between the crystalline state and the amorphous state caused locally by irradiation with a focused light beam. Such an optical information recording medium having a phase-change recording layer is being developed and used practically as a low cost large capacity recording medium excellent in portability, weather resistance, impact resistance, etc. For example, a rewritable phase-change type optical information recording medium (hereinafter “a rewritable phase-change type optical information recording medium” may sometimes be referred to as phase-change type optical disk, optical disk or disk) such as CD-RW, DVD-RW, DVD+RW and DVD-RAM is widely used. Further, it has been developed to achieve a high density by the use of blue laser or by an increase in NA of an objective lens, or to make high speed recording possible by improvement of the recording pulse waveform.
As a material for such a phase-change recording layer, a chalcogenide alloy is used in many cases. As such a chalcogenide alloy, a Ge—Sb—Te type, In—Sb—Te type, Ge—Sn—Te type or Ag—In—Sb—Te type alloy may, for example, be mentioned. Such an alloy is usually an overwritable material also.
Overwriting is a means wherein when recording is carried out again on a once-recorded optical information recording medium, writing is carried out without erasing before the recording, that is, a means of recording while erasing. On an optical information recording medium having a phase-change recording layer, recording is carried out usually by overwriting, and accordingly recording while erasing (i.e. overwriting) may sometimes be referred to simply as recording.
It is possible to obtain an optical information recording medium on which high velocity recording at 10-times velocity is possible by increasing the crystallization speed, by employing for the recording layer a composition which comprises as a matrix a Sb70Te30 alloy comprising a Sb70Te30 eutectic composition as the base and containing Sb in large excess, among the above chalcogenide alloys. Particularly, preferred for the recording layer is a composition which comprises a Sb70Te30 eutectic composition containing Sb in large excess and contains Ge (JP-A-2001-229537 (paragraph 0031)).